RF FEMs are used in wireless communication systems to process RF signals received from antennas and/or to generate RF signals for transmission over antennas. For example, RF FEMs in radio transmitters may be used to up-convert, amplify, and filter modulated baseband signals to the RF band. A critical component of RF FEMs is the power amplifier (PA). In many mobile wireless communication systems (such as WiFi, WiMax, 2G/2.5G/3G/4G, GSM/EDGE, WCDMA, LTE, TD-SCDMA used in handsets, smartphones, or tablets, etc.), a linearized power amplifier (LPA) with excellent performance is required. Due to the increasing complexity of multi-mode, multi-band capable mobile devices like smartphones, LPAs need to meet stringent performance requirements of high power (for long distance communication), high linearity (for high fidelity to enable high data rate communication), and high efficiency (for long battery life of mobile devices). In addition, LPAs or LPA modules need to be low cost and compact to enable their use in an ever wider array of mobile devices.
Conventionally, LPA modules or RF FEMs use a laminate design approach. The laminate design for a LPA module (or more generally PA module (PAM)) or RF FEM product needs a multi-layer substrate to incorporate active devices such as the PA die, low-noise amplifiers (LNA), or switches (e.g., single-pole multi-throw (SPXT)), and passive components such as resistors/inductors/capacitors (R/L/C) packaged in surface mount devices (SMDs) for PA input or inter-stage or output matching, biasing, bypassing, DC blocking, etc. The multi-layer substrate may also incorporate passive filters (surface acoustic wave (SAW) or bulk acoustic wave (BAW) filters), or duplexer or diplexer parts. The laminate substrate for a PAM or FEM product typically needs 4-6 layers depending on the complexity, since it needs to embed these active and passive devises, SMD components, and may be RF switch command lines, couplers, etc., inside PAM or FEM package. Therefore, the PAM or RF FEM product using this multi-layer substrate package will be expensive due to the high substrate cost and the cost for the passive SMD parts. The package is also thick and bulky due to the multi-layer substrate. In addition, the cost for assembling the package is high due to a dual assembly process for both die attaching and wire bonding for die assembly, and the SMD part assembly using solder reflow. As such, there is a need for a package for the PAM or RF FEM product that is low cost, compact and low profile.
Embodiments of the present disclosure and their advantages are best understood by referring to the detailed description that follows. It should be appreciated that like reference numerals are used to identify like elements illustrated in one or more of the figures.